1. Field of the Invention
The present invention relates to logging equipment, and more specifically, to remote controlled skyline logging carriages. The invention further relates to a grapple on a logging carriage that is operated by a towline.
2. Related Art
The traditional concern of a logging operation is the efficient and cost effective transportation of felled timber from a forest to the processing plants. In recent years, modern loggers are also concerned with minimizing the safety hazards and environmental damage resulting from logging. Thus, loggers may opt to selectively harvest timber instead of clear cutting, because clear cutting typically requires expensive electrically- or diesel-powered carriages. Therefore, it is important that modern logging equipment be designed to be used in either clear-cutting or selective harvesting situations. Also, it is important to design logging equipment that is easy and inexpensive to manufacture.
When harvesting logs along, or at the bottom of, steep slopes or hauling logs over longer distances, a cable yarding system is often employed, in which a cable known as a skyline is stretched between two spars to extend over sloped terrain; one spar is at a higher point than the other. One of the spars is usually a yarder or yoader (an excavator-based cable yarder without guylines to stabilize the machine itself
(http://www.cbs.state.or.us/external/osha/pdf/grants/osu/evaluatesynthroperigging.pdf)). A carriage equipped with grooved wheels or “sheaves” rides on the skyline cable to carry logs to a landing position near one of the spars. A landing is a generally level area, situated near a logging road, at which logs are debarked and delimbed and loaded on trucks and hauled to processing plants. Typically, a second cable, known as a towline, skidline, or mainline, extends from the uphill spar to the carriage. The towline is reeled in to pull the carriage uphill, and paid out as the carriage moves downhill due to gravity. The skyline system may comprise additional lines, such as a haulback line separate from the skyline or towline (see U.S. Pat. No. 3,695,672). The addition of multiple lines results in the need for additional drums on the yarder for tensioning and slackening the lines. Additional drums increase the complexity and the capital cost of the yarder, and the increased complexity requires a greater skill level on the part of the worker.
The present invention relates to two-drum cable yarding systems in which the yarder includes a first drum or winch connected to the skyline cable. The first winch pays out the skyline cable to lower the skyline and, at the same time, the carriage is allowed to roll by gravity down the skyline. The yarder also includes a second drum or winch connected to a towline cable, and, as the skyline is being lowered, the carriage is pulling out the towline. Once the carriage is lowered toward the logging area due to gravity and the lowering of the skyline, it is secured at a desired location, usually by means of a brake that fixes the carriage in position relative to the skyline and by control of the first winch to stop payout of the skyline. When it is time to bring the log(s) back to the landing, the towline is pulled back toward the yarder using the second winch, and the skyline is also raised and pulled back toward the landing, resulting in the carriage and logs being raised and pulled back to the landing.
In cable yarding, the carriage may be fitted with a grapple which closes around the log to pick the log up and bring it back to the landing. The use of grapples has reduced the number of workmen required on the slope or in the valley securing the logs with chokers (steel cables used for yarding logs). However, one of the problems existing in the field of carriages having grapples is how to minimize the cost and the operation of the grapple to effectively and inexpensively pick up the log and convey it to another desired location and then release it. There are grapple carriages that use a diesel engine inside the carriage to operate the carriage and the grapple; however, engine-powered grapple carriages are very expensive to manufacture.
In order to reduce the cost of manufacturing a grapple carriage, loggers have designed grapple carriages that use only pulleys and lines to operate the carriage and grapple. For example, Mitchell (U.S. Pat. No. 3,695,672), discloses a carriage 210 mounted on a skyline 212 and a pair of cables 238 and 236 which each extend over a pulley within the carriage. Cable 236 is used to operate the grapple, and cable 238 is used to pull the carriage 210 back to the landing. While this grapple carriage eliminates the need for a diesel engine, it requires a three-line system to operate the grapple and carriage, which necessitates three drums on the yarder, in turn adding to the expense of the logging operation.
In order to reduce the cost of the yarder, loggers have preferred to use two-line systems in which there is a skyline and a towline or mainline. Mitchell (U.S. Pat. No. 3,540,770) discloses a grapple carriage that is suspended from a skyline, wherein a mainline is connected with the carriage for moving it along the skyline. Although Mitchell uses only this two-line system (skyline and mainline) for moving the carriage between the landing and the logs, Mitchell must use an additional line inside the carriage to operate the grapple. This cable is mounted to the housing of the carriage and extends down through a grommet or adapter in the bottom wall of the carriage and connects with the grapple. An internal combustion engine, a storage battery, and an FM radio receiver in the carriage are used to operate the cable to open the grapple. When the cable is released, the normal weight of the jaws will cause the jaws to move inwardly due to the normal force of gravity, and the jaws will close. The internal combustion engine is very expensive. Additionally, the power used to operate the grapple is only the power that can be generated by the internal combustion engine and the cable connected inside the carriage. The loggers do not want the carriage to be too large; therefore, they require a small engine and the power generated is often insufficient to open a grapple, especially a grapple that is large enough for a turn of multiple logs.
Therefore, there is still a need for an inexpensive grapple carriage that does not require an internal combustion engine. The inventor believes that a grapple carriage is needed that does not require a third line to operate the grapple and that can be operated by one person.